1. Field of the Invention
The present invention relates to a method of manufacturing a metal workpiece, and especially a steel workpiece, by cutting a metal product, such as a plate or a block, by oxygen-cutting.
2. Discussion of the Background
In order to produce large boiler-construction components or heavy-mechanical components such as press platens or large magnets for a particle accelerator, blanks of workpieces whose shapes approach the final shapes desired are cut, by oxygen-cutting, from plates whose thickness ranges from 300 mm to 2 m. This cutting is performed by using an oxy-gas torch producing a heating flame obtained by combustion of a fuel gas in the oxygen, and a jet of gaseous or liquid oxygen, which cuts the metal and makes it burn. When the oxygen jet is gaseous, this jet is a hard jet, that is to say one obtained by a high-pressure supply.
This technique has a drawback resulting from this, namely that the quality of the cutting is poor and becomes increasingly poorer as the cut thickness increases. Among the defects which appear, there are especially:
a melting of the intersecting edge, on the same side as the torch, which creates a rounded edge whose radius is approximately 20 mm, for a thickness of 800 mm; PA1 defects of verticality of the workpiece resting on one of its faces which are manifested by deviations from verticality of from 12 to 15 mm, which corresponds to the direction, perpendicular to the faces of the workpiece, in which the thickness is measured; PA1 striations formed on the surface of the cut, whose depth reaches 5 mm; at the bottom of the cut, the striations are inclined and their depth may reach 8 mm; PA1 hot-spots, corresponding to zones in which a local combustion excess, and therefore a hollowing at the surface of the cut, occurs; PA1 the profile according to which the cutting is to be carried out is poorly followed; the tolerance is generally from 20 to 30 mm for a thickness of 800 mm. PA1 a central channel arranged on the axis of the cylindrical body emerging, at one of its ends, on the outlet face of the nozzle and, at its other end, on the connection surface in the region of a central chamber of the distributor, PA1 a first plurality of channels parallel to the axis of the nozzle and arranged on the periphery of the nozzle emerging, on the outlet face of the nozzle, into an annular zone having for axis the axis of the nozzle via a first outlet end and having a second end emerging at the connection surface into a first annular chamber of the distributor, this chamber being delimited on the connection surface by a first annular groove coaxial with the nozzle; PA1 a plurality of channels which are inclined in relation to the axis of the nozzle and are equal in number to the channels of the first plurality of channels, and which are arranged towards the outside of the nozzle in relation to the channels of the first plurality of channels, each emerging into a channel of the first plurality of channels via a first end and on the connection surface via a second end, inside a second chamber delimited on the connection surface by a second annular groove coaxial with the nozzle, characterized in that the nozzle furthermore includes: PA1 a second plurality of channels parallel to the axis of the nozzle emerging, at one of their ends, on the outlet face of the nozzle, into an annular zone having for axis the axis of the nozzle and located between the outlet end of the central channel and the annular zone into which the outlet ends of the channels of the first plurality emerge and, at their other ends, in a chamber of the distributor, this chamber being delimited on the connection surface of the nozzle by a third annular groove coaxial with the nozzle. PA1 it is obtained with its final dimensions by oxygen cutting a metal product without machining by removal of chips in its non-functional zones, and it has in the rough cutting state: PA1 a radius R, characteristic of the intersecting-edge melting of the workpiece, of less than 8/1000 of the thickness of the workpiece, PA1 a deviation from verticality V of less than 8/1000 of the thickness of the workpiece, PA1 vertical cutting striations which are uniform and have a depth of less than 1/1000 of the thickness of the workpiece, PA1 a mean rugosity of less than 20 .mu.m+20 .mu.m.times.e, e being the thickness of the workpiece expressed in meters, and the vertical direction corresponding to the direction, perpendicular to the opposite faces of the workpiece, in which the thickness is measured.
These defects make it necessary to provide additional thicknesses of metal of from 40 to 50 mm over the entire profile and to remove these overthicknesses by machining with a machine tool, which is very costly given the size of the workpieces.
The cutting is not good and in particular it forms inclined striations because the oxygen jet lacks power beyond a certain cutting depth.
It has been proposed in German Patent Application DE-A-1,927,523 to surround the oxygen-cutting jet by a sleeve of additional gas; in German Patent Application DD-A-71271 and in European Patent Application EP-A-O,255,430 it is proposed to surround the oxygen-cutting jet by a sleeve of a mixture of oxygen and fuel gas, and in all cases to surround the whole assembly by a heating ring. However, these techniques, although enabling the productivity of the cutting to be increased, do not solve the problem of the cutting quality,